Additives for molten metals



United States Patent 3,078,531 ADDITIVES FOR MOLTEN METALS Wilbur T.Bolkcom and William E. Knapp, Allison Park,

Pa., assignors to American Metallurgical Products Company, Pittsburgh,Pa.

No Drawing. Filed Oct. 5, 1960, Ser. No. 60,551 5 Claims. (Cl. 22-215)This invention relates to additives for molten metals and particularlyto additives and methods for making additions of organic fluorides tomolten metals and is a continuation-in-part of our copending applicationSerial No. 632,005, filed January 2, 1957, now abandoned. Theelimination of impurities in the form of inclusions and dissolvedmaterials has long been a problem in the metal industry. For example,the removal of gases such as hydrogen and the fluxing of inclusionscauses heavy losses in metal production because of the necessity ofremoving and discarding large portions of ingots in order to eliminatethese undesirable components. We have found that solidpolytetrafluorethylene may be used in molten metals for reducing thecontent of undesirable gases, increasing the fluidity of the moltenmass,fluxing and eliminating both high and low melting point inclusions andimproving the surface conditions of the resulting solidified metal. Thesubject of this invention can perhaps be best understood by reference tothe following examples:

Example I About three ounces per ton of small pebbles ofpolytetrafluorethylene were placed in the bottom of an uncoated ingotmold in four-ounce bags. A cover plate was fitted over the ingot mold torestrict the opening into the mold to a 6" diameter opening. Moltensteel was teemed into the mold through the hole in the cover plate ontothe pebbles of polytetrafluorethylene. Black smoke began to appearalmost at once and continued as teeming progressed. When the black smokeappeared to be diminishing, additional pebbles of polytetrafluorethylenewere added by throwing them in through the opening in the cover plateuntil a total of about five ounces per ton had been added. The resultingingot was compared with a similar ingot poured in the usual fashion. Theingot treated according to the above described process had much lesstitanate and aluminate inclusion and yielded about 60% to 65% of theingot as shippable quality as compared with about 45% for theconventional ingot.

Example II Steel was poured into an uncoated ingot mold in the usualmanner. During pouring annular rings of polytetrafluorethylene wereadded. The rings were added by means of a device such as thatillustrated and described in our copending application Serial No.632,110 filed January 2, 1957, now abandoned. An annular ring ofpolytetrafluorethylene is mounted on the end of a bar of steel by meansof a bolt passing through the central opening of the ring andthreadingly engaging the end of the steel bar. An enlarged steel portionis provided on the opposite end of the steel bar to add weight andstability to the unit so that the ring of polytetrafluorethylene may besatisfactorily positioned in the molten metal.

Example III A Phosphor bronze containing 90% copper and 10% aluminum wastreated with approximately 4 ounces of 3,078,531 Patented Feb, 26, 1.963

drogen, after treatment the same bronze contained only 6' parts permillion of hydrogen. The treated bronze was denser and free fromporosity as well as being much more flowable than the untreated bronze.

We have found that the practice of our invention will reduce thehydrogen and oxygen, increase fluidity, in, crease yields and providebetter surface conditions in steel in both hot and cold conditions. Wehave also found that the additive of our invention has particularadvantage in the magnesium industry in promoting a finer and moreconsistently controlled grain size.

We believe that the surprising success of our treatment results from twotypes of effects: (1) Physical effects such as the replacement of oxygenin the ingot mold by an active gas contained within the cover plate andthe elfect of gas escaping through the cover plate around the teemedstream of metal so as to form a protective shield while the metaltravels between the ladle and the ingot and increased fluidity orreduced surface tension so that high melting point inclusions levitate,and (2) Chemical effects such as reaction with and reduction innitrogen, oxygen and hydrogen in the metal. These effects all appear tobe supported by the physical indications and appearance of steel ingots.Successful treatment according to our invention is accompanied byextraordinary amounts of dirt, dross and like refuse coming to the topof the molten ingot, indicating that the polytetrafluorethylene has notsimply formed a protective atmosphere but has entered into a chemicalreaction with the oxygen, nitrogen and hydrogen carried from the furnaceand otherwise forming undesirable inclusions in the steel. This is ahighly desirable result, not achieved by merely casting in a protectiveatmosphere but achieved by the practice of our invention. Uponstripping, the ingot will have an extraordinary smooth skin. Comparisonof treated and untreated ingots shows a great difference in acid solubleand insoluble titanium, aluminum and zirconium. We accordingly believethat our theory is correct but do not wish to be bound thereby.

We have foundv that the use of polytetrafluorethylene as describedherein will produce improved surfaces on metal ingots thus requiringless conditioning and better yields. We have also found that there is avery marked reduction in inclusions and in the elimination or control ofhydrogen and oxygen.

While we have set out certain preferred practices and materialsaccording to our invention, it will be understood that the invention maybe otherwise practiced within the scope of the following claims.

We claim:

1. A method of treating metals to improve fluidity and reduce inclusionscomprising the steps of teeming the molten metal in the usual mannerthrough the atmosphere and free from previous inert gas and fluoridepurge into a mold open to the atmosphere and free of inert gas coverthrough a restricted opening in the mold and add ing to the metal duringteeming in the mold about /2 oz. to about 8 oz. of solidpolytetrafluorethylene per ton of metal.

2. A method of treating steel to improve fluidity and reduce inclusionscomprising the steps of teeming the molten metal in the usual mannerthrough the atmosphere and free from previous inert gas and fluoridepurge into a mold open to the atmosphere and free of inert gas coverthrough a restricted opening in the mold and adding to the metal duringteeming in the mold about 4 oz. of solid polytetrafluorethylene per tonof metal.

3. A method of treating metals to improve fluidity and reduce inclusionscomprising the steps of teeming the molten metal into a mold in theusual manner through the atmosphere and free from previous inert gas andfluoride purge into a mold open to the atmosphere and adding to themetal during teeming about 6 oz. to about 8 oz. ofpolytetrafiuorethylene per ton of metal.

4. A method of treating i'netals to improve fluidity and reduceinclusions comprising the steps of teeming the molten metal in the usualmanner through the atmosphere into a mold open to the atmosphere andcontaining about /2 oz. to about 8 oz. of solid polytetrafiuorethyleneper ton of metal whereby the solid polytetrafluorethylene is fused andgasified and reacts with inclusions in the metal to remove them as themetal is teemed.

5. A method of treating metals to improve fluidity and reduce inclusionscomprising the steps of teeming the molten metal in the usual mannerthrough the atmosphere into a mold open to the atmosphere and adding tothe molten stream entering the mold about /2 oz. to 8 oz. of solidpolytetrafluorethylene per ton of metal.

UNITED STATES PATENTS Wright July 12, 1910 Stroup Apr, 23, 1935 StroupOct. 6, 1936 Webbere Nov. 20, 1956 FOREIGN PATENTS Austria Aug. 24, 1951Belgium June 30, 1951 Great Britain Mar. 19, 1931 Great Britain June 10,1948 Great Britain Oct. 29, 1958

1. A METHOD OF TREATING METALS TO IMPROVE FLUIDITY AND REDUCE INCLUSIONSCOMPARSING THE STEPS OF TEEMING THE MOLTEN METAL IN THE USUAL MANNERTHROUGH THE ATMOSPHERE AND FREE FROM PREVIOUS INERT MANNER THROUGH THEATMOSPHERE A MOLD OPEN TO THE ATMOSPHERE AND FREE OF INERT GAS COVERTHROUGH A RESTRICTED OPENING IN THE MOLD AND ADDING TO THE METAL DURINGTEEMING IN THE MOLD ABOUT 1/2 OZ. TO ABOUT 8 OZ. OF SOLIDPOLYTETRAFLUORETHYLENE PER TON OF METAL.